1. Field of the Invention
The present invention relates to a hydraulic damping device, and more particularly to a hydraulic damping device for preventing the transmission of vibrations of wide-ranging frequencies having a simple construction.
2. Description of the Related Art
A hydraulic damping device employed as an engine mount for a vehicle, is required to absorb idle vibrations occurring when an engine is idling, and to restrain shake vibrations occurring while the vehicle is running. In order to absorb the idle vibrations, the spring constant of the device must be decreased, and in order to restrain the shake vibrations, the damping coefficient of the device must be decreased.
U.S. Pat. No. 4,700,933 discloses a hydraulic damping device wherein the transmission of the above-described idle and shake vibrations have been prevented by varying the cross-sectional area and length of the passageway for a damping liquid by the operation of valve means.
U.S. Pat. No. 4,610,421 discloses a hydraulic damping device wherein idle and shake vibrations are prevented by controlling the opening and closing of an orifice by valve means.
However, the size of the above-referenced damping devices provided with valve means becomes large, and is difficult to be used, since the engine mount must be installed in a limited space within an engine compartment.
U.S. Pat. No. 4,583,723 and U.S. Pat. No. 4,635,910 disclose fluid damping devices having electromagnetic devices arranged within the damping device, thus, increasing the overall size of the damping device which makes it difficult to use within an engine compartment.